ASTM A790 Specification Scope and Applications
ASTM A790 specification covers seamless and straight-seam welded ferritic/austenitic stainless steel pipe, primarily intended for general corrosive service, with particular emphasis on resistance to stress corrosion cracking. These steels are prone to embrittlement when used for prolonged periods at elevated temperatures.
In addition to the dimensions of welded and seamless stainless steel pipe shown in ANSI B36.19, pipes of other dimensions may also be supplied, provided they meet all other requirements of ASTM A790.
Ordering Information
When ordering material under this ASTM A790 specification, the following details should be included to fully describe the desired material:
- Quantity (in feet [meters] or number of lengths),
- Material name (ferritic/austenitic stainless steel pipe),
- Manufacturing process (seamless or welded),
- Grade (see Table 1),
- Size (NPS designation or outside diameter and schedule number of average wall thickness),
- Length (specific or random) (see Section 11),
- End finish (refer to Section on ends of ASTM A 999/A 999M),
- Optional requirements (product analysis, Section 9; hydrostatic test or nondestructive electric test, Section 14),
- Test report required (refer to certification section of ASTM A 999/A 999M),
- Specification designation,
- Special requirements and any supplementary requirements selected.
Materials and Manufacture
Manufacturing Process:
- The pipe shall be manufactured using a seamless or automatic welding process, with no addition of filler metal during the welding operation.
- The pipe may be either hot-finished or cold-finished at the manufacturer’s option.
- The pipe shall be pickled to remove the scale. If bright annealing is used, pickling is not necessary.
- Unless otherwise specified in the order, all pipes shall be supplied in the heat-treated condition as shown in Table.
Heat Treatment for Seamless Pipe:
For seamless pipe, as an alternative to final heat treatment in a continuous furnace or batch furnace, the pipe may be individually quenched in water or rapidly cooled by other means immediately following hot forming, provided the pipe temperature is not less than the specified minimum solution treatment temperature. This does not apply to UNS S32950, which shall be air-cooled.
No Heat Treatment after Welding:
If the purchaser requests pipe without heat treatment after welding, the following conditions must be specified in the purchase order:
For pipe made from a plate that has already been heat-treated according to Table 1 for the particular grade, no final heat treatment is required, provided a sample from the batch of finished pipe or material, representing the heat of pipe, passes the A 923 Method B or C test (see Note 2), including base metal, weld metal, and heat-affected zone for each heat. Each pipe supplied under this provision must be marked with the suffix “HT-O”.
The HT-O provision does not apply to materials not listed in Table 3 of Test Methods A 923.
Note 2: The A 923 test method (B or C) is at the manufacturer’s discretion unless otherwise specified by the purchaser.
Chemical Composition
Each heat of steel must be analyzed by the steel manufacturer to determine the percentage content of specified elements.
![Chemical Requirements[A]](https://ssmalloys.com/wp-content/uploads/2024/11/Chemical-RequirementsA.jpg)
Tensile and Hardness Properties
The material shall conform to the tensile and hardness properties prescribed in Table
Lengths
Pipe lengths shall conform to the following standard practices:
Unless otherwise agreed, pipes from NPS 1/8 to and including NPS 8 are available in lengths up to 24 feet (see Note 3), with a permissible range of 15 to 24 feet (see Note 3). Short lengths are acceptable, and the number and minimum length must be agreed upon by the manufacturer and purchaser.
Note :This value applies when the inch-pound units are used for purchase. If the M designation of this specification is the basis for purchase, the corresponding metric values should be agreed upon between the manufacturer and purchaser.
If specific cut lengths are required, the required lengths should be specified in the order. No pipe shall be shorter than the specified length, nor exceed 1/4 inch [6 mm] over it.
Unless otherwise specified, no pipe joints are allowed.
Repair by Welding
- For welded pipe of size NPS 6 or larger, with a specified wall thickness of 0.188 inches [4.8 mm] or more, repairs may be made to the weld seam with the addition of compatible filler metal. The repair procedure must follow the guidelines for plate defect repairs as outlined in the Repair by Welding section of ASTM A 999/A 999M.
- The length of the repair to the weld seam shall not exceed 20% of the total seam length.
- Weld repairs must be made using the gas tungsten arc welding process and with the same classification of bare welding rod that is qualified to the most recent AWS Specification A5.9 for the grade of pipe being repaired, as per Table 4.
- With the purchaser’s approval, weld repairs may use a more highly alloyed filler metal than the base metal if needed for corrosion resistance or other properties.
- Pipes that have been repaired with filler metal must be marked with the “WR” symbol and noted in the test certificate. If a filler metal other than the one listed in Table 4 is used, it must also be identified in the certificate.
- Weld repairs must be completed prior to any heat treatment.
Dimensions of Welded and Seamless Stainless Steel Pipe
FAQ
ASTM A790 is a standard specification that covers seamless and welded ferritic/austenitic stainless steel pipes. These pipes are commonly used in high-temperature, high-pressure applications and environments involving corrosive media.
ASTM A790 covers duplex stainless steel pipes, which are a mix of austenitic and ferritic stainless steels. These pipes offer enhanced strength and corrosion resistance compared to standard austenitic steels.
- ASTM A790 specifically covers duplex and super duplex stainless steel pipes, while ASTM A312 covers austenitic stainless steel pipes.
- ASTM A790 pipes are designed for more aggressive environments, such as those involving chloride stress corrosion cracking.
Compared to other duplex stainless steel standards (like ASTM A276 or ASTM A923), ASTM A790 is specifically for pipes, making it more focused on applications requiring pipe-form materials with higher strength and resistance to corrosion, especially in challenging environments.
Yes, welding is permitted for ASTM A790 pipes, including both seamless and welded pipes. However, welding requires careful attention to avoid weakening the pipe’s corrosion resistance. Preheat and post-weld heat treatment are often required, especially for the super duplex grades.
